APPARATUS FOR PRODUCING GASEOUS FISSION PRODUCTS, PARTICULARLY Xe{14 133

ABSTRACT

Gaseous fission products are produced by bombarding a suitable element with neutrons. The element is enclosed in a gas-tight container during the neutron bombardment. When the desired quantity of the gaseous fission product has been produced, the container is opened and the gaseous phase in the container is brought to flow to an apparatus in which the desired fission product is separated.

United States Patent Schmeling 1 Aug. 1, 1972 [54] APPARATUS FOR PRODUCING GASEOUS FISSION PRODUCTS,

PARTICULARLY XE133 [72] Inventor: Per Erik Schmeling, Nykoping,

Sweden [73] Assignee: Aktiebolaget Atomenergi,

Stockholm, Sweden [22] Filed: April 14, 1969 [21] Appl. No.: 815,919

[52] US. Cl. ..55/208, 55/387, 176/16 [51] Int. Cl. ..G2lg l/00 [58] Field of Search ..176/10-16, 68; 55/208, 387

[56] References Cited UNITED STATES PATENTS 3,079,317 2/1963 Jenks et a1. ..176/15 3,135,665 6/1964 Koutz et a1 ..176/68 X 3,365,371 1/1968 Lass et a1. ..176/68 X 3,446,703 5/1969 Lyons et a1 ..176/68 X OTHER PUBLICATIONS Second Geneva Conference, 1958, Vol. 20, pp. 33. ORNL- 3802, 1964, pp. 5,6,25,26,52.

ORNL- 3840, 1966, pp. l- 5.

ORNL- 3633, 1964, pp. 19, 78- 80, 157- 159.

Primary Examiner-Carl D. Quarforth Assistant Examiner-Harvey E. Behrend Attorney-Pierce, Scheffler 8L Parker [57] ABSTRACT Gaseous fission products are produced by bombarding a suitable element with neutrons. The element is enclosed in a gas-tight container during the neutron bombardment. When the desired quantity of the gaseous fission product has been produced, the container is opened and the gaseous phase in the container is brought to flow to an apparatus in which the desired fission product is separated.

1 Claim, 4 Drawing Figures PATENTEDAus 1 1912 SHEET 1 OF 3 Fig.1

PRTENTEDAUQ 1 I972 SHEET 3 BF 3 Fig.4

APPARATUS FOR PRODUCING GASEOUS FISSION PRODUCTS, PARTICULARLY XE-l 3 3 The invention is concerned with a method of producing gaseous fission products by bombarding (irradiating) a target with neutrons, said target containing an element which, on being thus bombarded, produces the desired gaseous fission product. The invention is particularly concerned with the production of gaseous fission products from uranium.

It has been known for several years that nuclides can be produced from uranium which has been bombarded with neutrons. It is a characteristic feature of the conventional processes that a target containing the uranium as a metal, an alloy, or a chemical compound is bombarded with neutrons in a nuclear reactor. The irradiated target is dissolved chemically. The gaseous fission products, i.a. Xe-133, and the other gases then released are purified. The radioactive rare gases are separated in the final purification step. The solution thus produced contains a large number of radioactive elements, and is processed according to various methods. One such method is, for instance, the production of 1-131 and Xe-l 33 described in a publication of the Oak Ridge National Lab., viz. ORNL-3633, pp. 77-80 and 151-159, respectively. It is also known to use as a target a uranium salt which is readily soluble in water and after the bombardment with neutrons the salt can be dissolved without the necessity of using a complicated chemical apparatus. Such water soluble salts, however, are not used for the production of large quantities of radioactive nuclides, because they have a tendency of decomposing chemically on being bombarded with neutrons, and because particular consideration must be given to the canning of the material also with regard to the removal of the heat of fission.

It is the object of the invention to provide a method for the commercial production of the gaseous nuclides in a way less complicated and more reliable than the known methods, so as to avoid the contamination of the gaseous nuclides with foreign gases such as air, water vapor, nitrous gases.

The characteristic feature of the invention is that the target is enclosed in a gas-tight way in a, preferably evacuated, container, and is there bombarded with neutrons of an adequate energy level for the production of the desired nuclide, for a time sufficient for the production of the desired quantity of the nuclide, and that the container is subsequently opened and the desired nuclide or nuclides are recovered from the gaseous phase. The container is preferably opened in a closed, evacuated system, which may contain a sorption agent, such as activated carbon, and/or a distilling apparatus for the sorption or separation of the desired nuclide. In order to increase the yield of the process the target should preferably be bombarded under conditions promoting the gas diffusion in the target. Therefore, all parts of the major portion of the solid substance of the target should preferably be at a lesser distance from the continuous gaseous phase in the container than one-tenth of the thickness of the target body. This can be achieved if the target is used in the form of grains, a powder, or one or more foils or porous bodies, resulting in shorter paths of diffusion in the solid phase to the continuous gas phase in the container extending into the target body. The diffusion can also be promoted by bombarding the target at an increased temperature.

According to a preferred embodiment of the invention the container and the target contained therein is preferably heated so that the target melts, resulting in the gaseous nuclide and other gaseous substances, if any, being released from the melt and transferred to the gaseous phase. The container is subsequently opened, preferably after the target has solidified, and the nuclide is recovered.

The invention will now be explained with reference to an example, in which the nuclide Xe-l33 is produced from uranium. A target is prepared from such a uranium compound that alone or possibly admixed with auxiliary agents, such as fiuxing agents, renders the target a comparatively low melting point, so that the target can be molten without damaging the container, which preferably consists of steel. The target should preferably also be readily soluble in water, so that it can be processed in a convenient way after the bombardment. The target is usually prepared by melting a uranium compound together with other components, and is referred to hereinbelow as a uranium melt.

The uranium melt is preferably bombarded with neutrons while being enclosed in a steel container. After the bombardment the steel container, while still closed, is heated to a temperature above the melting point of the uranium melt. After cooling the rare gases are present in the gaseous phase, together with minor impurities consisting of elements having a high vapor pressure, such as iodine. The container is now opened in a closed, evacuated system, and the rare gases can be removed without any risk of being contaminated by other fission products or by water vapor or such gases as are normally created when a target is dissolved according to known methods.

An example of a uranium melt is the mixture of various molten salts which is produced by dissolving U0 in molten sodium pyrosulfate. This uranium melt can readily achieve a content of 30 percent by weight of uranium. It has a melting point of 500600 C, and is readily soluble in water. Other known mixtures of molten salts, containing uranium, which have been suggested to be used as nuclear fuel in nuclear reactors of the molten-salt type, can be used according to the invention.

Experiments have been made with bombarding the uranium sodium pyrosulphate melt referred to above with neutrons. The melt was bombarded in an evacuated steel container, which was subsequently heated to 600 C, and was then left to cool. The container was now opened under vacuum, and the released rare gas passed to a so called carbon trap in which it was adsorbed on activated carbon cooled by means of liquid nitrogen. The carbon trap contained nearly pure Xe-l 33 and minor quantities of l(r and 1-1 31 as impurities. On careful heating of the carbon trap the rare gases will be desorbed, while the iodine is retained in the trap. The described method is convenient for the manufacture of Xe-l 33.

The neutron bombardment and the subsequent heating, if any, usually results in a strong heating of the target. Therefore, the material of the container must respond to high demands, and, therefore, steel containers have been used, for example in the experiments referred to above. A temperature increase can be counteracted by means of cooling coils in the container, if desired in the very target, in a manner known per se.

Another example of a nucleid which can be produced according to the invention is the radioactive isotope Ar-37, which is produced by bombarding calcium or a calcium compound with neutrons according to the formula (Ia-40 (n, a) Ar-37.

The target may for instance consist of mixed crystals of NaF-CaF of NaClCaCl which are comparatively stable during the bombardment, and which melt at a comparatively low temperature. The NaCl-CaCl crystals have an entectical point when the percentage of NaCl is 32 percent by weight, resulting in a melting point of approximately 500 C.

Another example is the production of tritium, H-3 by the nuclear reaction The target may for instance consist of mixed crystals of LiCl-NaCl or LiClCaCl The latter crystals have an entectical point when the percentage of CaCl is 64 percent by weight resulting in a melting point of approximately 505 C.

The accompanying drawings illustrate the invention.

FIG. 1 illustrates a nuclear reactor for bombarding a target with neutrons.

FIG. 2 illustrates an apparatus for removing the desired gaseous fission product from the target.

FIG. 3 is an exploded view of a container for the target and the means for opening the container.

FIG. 4 illustrates the container and a plug with a needle for piercing the wall of the container.

The nuclear reactor of FIG. 1 comprises a reinforced concrete vessel 1, a steel vessel 2, in said steel vessel a reactor core 3 containing the fissile fuel, and a tube 4 extending into the reactor core. A container 5, containing the target, is inserted into the reactor core 3 through the tube 4 and is bombarded with neutrons for a desired time.

The container 5 is now placed in a lead container 6, the central opening 9 of which contains a heating coil 10. The container has a lead plug 7 through which extends a rod 8 working as a screwdriver. The container 5 heated until the target 23, see FIG. 4, has molten. The rod 8 is now inserted into an opening 24 in a plug 25 having screw-threads fitting into those of a recessed portion 26 of the container 5. The plug 25 is screwed down until a needle 27 in the bottom of the plug pierces the bottom 28 of the recessed portion 26.

The gaseous fission products flow the opening thus produced, through the screw-threads of the plug 25 and the recessed portion 26 (said screw-threads not being entirely tight), through an opening 11 in the lead container 6, and through a tube 12 to a cooled carbon trap 14, enclosed in a container 15 having inlets and outlets l6 and 17 for liquid nitrogen or a heating agent. When the gas has been absorbed in the cold carbon trap 14 the valve 13 is closed and the carbon trap is heated. The tube 21 is connected to a vacuum pump to remove air, for instance. The valve 29 is now closed, and the carbon trap 14 is further heated, resulting in that the desired gaseous fission product leaves the carbon trap. The pressure is indicated by the pressure gauge 22. The gas is removed through the tube 21. If desired, the valve 30 is opened, making the carbon trap 14 commucate with at be 18 containi a nesium The tube 1% IS contame m a contalner fieii so contaming a heating coil 20. The magnesium is useful for removing S0 for instance, from the desired gaseous fission product.

What is claimed is:

1. An apparatus for collecting a gaseous fission product produced in a target when exposed to a neutron bombardment in a nuclear reactor to produce fission reactions resulting in said fission product, said apparatus comprising a target (23);

a container (5) for the target;

a recessed wall portion (26) in said container;

a screw-thread in said recessed wall portion;

a screw-thread plug (25) engaging the screw-thread of said recessed wall portion;

a needle (27) supported by said plug so as to pierce a pierceable portion of said recessed wall portion; means (24) on said plug engageable by a tool (8) to rotate the plug;

a lead container (6) having a cavity (9) to receive said container;

heating means (10) in said cavity to heat said container and said target to release said gaseous fission product from said target;

said tool (8) extending through the wall of said lead container into said cavity so as to engage said plug; an escape canal (11) through the wall of said lead container for the escape of gaseous fission product released upon the heating of the target; and

a cooled carbon trap (14) communicating with said canal for absorbing escaping gaseous fission product. 

